Toolbox talk 6: Supervisor’s instructions
ASSET
INTEGRITY
Locked Open / Locked Closed Valves
This toolbox talk is designed to:
•Help your team understand the significance of a locked valve
and why it is locked
•Inform your team of the importance of following procedure
when changing the position of a locked valve
•Identify likely areas where locked valves might be
encountered on a facility
Carry out this toolbox talk before commencing a new
task/job involving a change in status of a Locked Open
or Locked Closed valve.
It is best to complete this talk in small groups – maximum ten
people. Additional information and training may be required at
the discretion of local management.
1)Give a copy of the Group Sheet to your group.
2)Using the flow chart given below discuss the process that
must be followed to change (and reinstate) the status of a
locked open / locked closed valve. Ask the Group to identify
who is the responsible person for each of the stages in the
process by marking or colouring the boxes as applicable.
3)Ask the Group to study the diagrams on the Group Sheet
showing the various classifications of LO/LC valve types.
Ask the Group to identify the hazard that might arise if
they move the valve from its status designated in the LO/LC
Register without applying suitable controls or mitigation.
4)Use the diagrams on the Group Sheet to discuss the
mitigations/controls that should be put in place prior to
moving the position of the LO/LC valves in each case.
5)At the end of the Toolbox Talk, provide the Group with their
own copy of the Supervisors Sheet for them to keep as a
reference; ‘Know the Process, Know the controls’.
6)Ask what the team should do if they become aware of any
improperly locked valves or broken locks (first step would
be to report them to their supervisor).
MAJOR HAZARDS AWARENESS
LO/LC valves – Flow chart of approval process
Start
Request approval to
change valve status
Confirm
classification
Identify Mitigation
and controls needed
Authorise and sign
LOLC register and
issue keys
Apply Mitigation
and Controls
Remote PA confirms
to Authorising
Authority controls
in place
Complete Task
Part of Isolation
Certificate
Yes
Update tags with
status change
Move valve
No
Approve
de-isolation
Part of Isolation
Certificate
Yes
Return valve to
normal position
Update tags with
status change
Remote PA confirms to Authorising
Authority Valve returned to normal
position and tags updated
Key
Performing
Authority
No
Authorising
Person
Apply Isolation TAG
to valve
Sign LOLC register
activities complete
-valve returned to
normal status
Toolbox talk 6: Supervisor’s instructions
Answers
1
PSV
2
LC
3
Vent/ flare/ LP system
Flare/Vent
LO
LO
Spec
Break
Spec
Break
LO
PCV
LC
NC
Blow down valve
LO
LO
LCV
Spec
Break
LO
?
Type A 1 & 2 Single PSV with
Isolation Valves
Hazard: There is a risk of loss of containment
if an over pressure event occurs and the PSV is
isolated from the system under pressure.
Mitigation: The system being protected should
be isolated and depressured before changing
from LO to LC.
4
Hazard: If the BDV is isolated when the
system is pressurised it will not be possible
to depressurise the system in an emergency.
This could lead to overpressure and loss of
containment in a fire event.
Mitigation: The system being protected should
be isolated and depressurised before changing
from LO to LC.
5
Vent/ flare/ LP system
LO
?
Type A 3 Blow down valve with
Isolation Valve(s)
Atmospheric
Vent
Air/
Hydraulics
LO
LC
LO
LO
HIPS / ESD
Trip function
transmitter
LO
LO
LO
Hazard: If a LC manual valve is opened when
the system is pressurised there is a risk of loss of
containment and uncontrolled discharge of gas,
hydrocarbons or toxic fluids.
Mitigation: The system to be depressurised /
drained should be isolated from the pressure
source before changing from LC to LO.
Mitigation: The system being protected should
be isolated and depressured before changing
from LO to LC.
?
To Vent/Flare Stack
LoLo/ Hi Hi
Level trips
LT
Corrosion
monitoring
Vent/Flare Header
Pilot gas
supply
LO
LO
Fiscal/critical
metering &,
Analysers
?
Hazard: If the PCV/LCV is isolated when the
system is pressurised there is a risk of loss
of containment if an over pressure / overfill
event occurs.
To Flare Pilot
Source of
pressure/fluids
Type A 5 Manual isolation from
vent, atmosphere or drains
Type A 4 Pressure/ Level Control
Valve with Isolation Valve(s) and
atmospheric vent
LO
PT
ESDV
LP system/
drains
LP system/
drains
6
LoLo/ Hi Hi
Pressure trips
LC
?
Atmospheric
Vent
Vent/Flare
KO Drum
Purge Gas
supply into
vent/flare
header
LO
LO
Type B Control of Safety Critical
Instruments and High Integrity
Protection Devices (HIPS)
Hazard: If manual valves are closed safety
critical devices will not function.
Mitigation: Over-ride process to be used with
risk assessment. The downstream primary SCE
to be fully functional keeping at least 1 barrier
in place.
?
Type C 1 Protection against
ingress of air/ gas into a system/
Equipment / flare purge systems
Hazard: If purge valves are closed there is a risk
that air will enter the vent allowing an explosive
atmosphere to develop inside the vent system
with a risk of internal explosion. If the pilot gas
valves are closed there is a risk of flare flame-out
resulting in (potentially toxic) process streams
being vented to atmosphere.
Mitigation: If no pilot gas; facility shutdown or
alternative flare ignition method in place. If no
purge gas; facility shutdown if no alternative
purge system available.
MAJOR HAZARDS AWARENESS
Toolbox talk 6: Supervisor’s instructions
Answers
7
8
ESD
9
LC
LCV/ PCV
LO
Pressurised
instrument
cabinet
LC
Plant/
Equipment
LC
LC
LC
Spec
Break
Air or Inert
Purge gas
LO
Spec
Break
Spec
Break
LC
LC
?
Type C 2 Protection against
ingress of gas into a Pressurised
instrument cabinets
?
Type D 1, 2 Protection of
Downstream Facilities against
adverse conditions
Hazard: If purge valves are closed and
flammable gas enters the cabinet there is a
risk of an internal explosion in the cabinet.
Hazard: Loss of control of volumes/pressure
can occur when by-passes/ start up lines are
left open.
Mitigation: Gas checks negative, power isolated,
Facility should be shutdown if no alternative
purge system is available and the instrument
cabinet is in a classified area.
Mitigation: Adherence to procedure and
isolation standards. (does not apply to
automatic start up facilities and by passes
controlled by PLC).
LT Spec
HT Spec
HT Spec
LT Spec
?
LO
Type D 3, 4, 6 Protection of
downstream facilities against
adverse conditions
Hazard: Open by passes have the potential
to increase flow / pressure on downstream
equipment and lead to loss of containment.
Exposure of downstream systems to
temperature extremes may cause low
temperature embrittlement, or weakened
material due to high temperatures.
Mitigation: Correct engineering design.
Specified Safe Operating Envelope limits.
Compliance with procedures. Valves should only
be opened when temperatures have normalised.
10
PSV
PSV
11
12
Non-Nace piping
LO
LO
Nace piping
INTERLOCK
LO
LC
LC
Spec
Break
Chemical
Storage
High H2S
Stream
FT
LO
LO
PT
LO
LO
Off Spec fluid
?
Type D 5 Protection against
adverse downstream conditions –
dual PSVs
Hazard: There is a risk of loss of containment if
an over pressure event occurs and both PSVs are
isolated from the system under pressure.
Mitigation: Interlock procedure used to ensure
one PSV is on line at all times.
?
LC
Type E 1, 2 Isolation valves
preventing off spec fluids
reaching downstream facilities
Hazard: Open valves would allow high H2S stream
to enter a non-Nace spec piping/ equipment
with potential for failure of equipment. Open
valves would allow off-spec fluid to mix with
on-spec fluids with potential for scale formation,
napthenates or off-spec product.
Mitigation: There are no circumstances where high
H2S should be allowed to enter non-Nace facilities.
Specified Safe Operating Envelope limits should
be applied. Off-spec fluid should only be allowed
to mix with on-spec fluids where appropriate
procedures and mitigations are in place.
LO
?
Type E 3 Protection of
Downstream Facilities Protected
by Chemical Injection
Hazard: Loss of protective chemicals
(e.g. corrosion inhibitor) can lead to
adverse downstream conditions and a
risk of loss of integrity.
Mitigation: Adherence to procedure and
isolation standards. Apply Management of
Change (MOC) procedures if changes required.
MAJOR HAZARDS AWARENESS